1. Field of the Invention
The invention relates to a semiconductor device and a manufacturing method thereof.
2. Description of Related Art
A semiconductor device is provided with a passivation film for protecting a semiconductor element. With a semiconductor device in which a metal layer (i.e., an electrode or wiring or the like) is formed on an insulating film, typically a passivation film is formed on the metal layer, and then an organic coating film (such as a polyimide) is formed, after which the device is packaged with resin or the like. In this case, a crack may form in the passivation film due to a change in the external temperature. That is, stress from the resin, the organic coating film, and the metal layer may cause stress to concentrate at a corner portion of the protruding metal layer, and a crack may form in the passivation film that covers this corner portion. Japanese Patent Application Publication No. 2011-114008 (SP 2011-114008 A) describes a semiconductor device that reduces the occurrence of cracking in the passivation film due to a change in temperature.
With the semiconductor device described in JP 2011-114008 A, aluminum wiring (i.e., a metal layer) is formed on a barrier layer (i.e., a passivation film), a cap metal (TiN or the like) is provided on an upper portion of this aluminum wiring, and a sidewall SiN or SiO or the like) is provided on a side portion of the aluminum wiring. Forming aluminum wiring above the barrier layer (i.e., the passivation film) enables the occurrence of cracking in the barrier layer (i.e., the passivation film) to be reduced.
With the semiconductor device described in JP 2011-114008 A, the area of the metal layer (i.e., the aluminum wiring) is surrounded by a film (hereinafter also referred to as a “coating”) that has a smaller linear expansion coefficient than the metal layer. When such a structure is heated to a high temperature (for example, if a polyimide baking process is applied during manufacturing), the metal layer will greatly expand, while the coating around the metal layer will not greatly expand. Therefore, the metal layer will plastic deform inside the coating, and the crystal density of the metal layer will consequently increase. Then when the structure returns to annual temperature, the metal layer of which the crystal density had temporarily increased will become smaller than the metal layer before being heated. As a result, a cavity (hereinafter also referred to as a “void”) that previously did not exist will end up being formed between the metal layer and the coating.